Difference Between Autotrophs and Heterotrophs

Main Difference – Autotrophs vs Heterotrophs

Autotrophs and heterotrophs are two nutritional groups found in the environment. Autotrophs produce their own food by either photosynthesis or chemosynthesis. Autotrophs are at the primary level of food chains. Hence, both syntheses are known as primary synthesis. On the other hand, heterotrophs consume autotrophs or heterotrophs as their food. Thus, heterotrophs are at the secondary or tertiary levels of the food chains. The main difference between autotrophs and heterotrophs is that autotrophs are capable of forming nutritional organic substances from simple inorganic substances such as carbon dioxide whereas heterotrophs are unable to produce organic compounds from inorganic sources.

What are Autotrophs

The organisms which produce complex organic compounds like carbohydrates, proteins and fats from simple compounds in the environment are known as autotrophs. This mechanism is referred to as the primary production. They process photosynthesis or chemosynthesis. Water is used as the reducing agent by both processes. But, some autotrophs use hydrogen sulfide as their reducing agent. Autotrophs are considered as the producers of the food chain. They do not require organic carbon as a living source of energy.

Classification of Autotrophs

Autotrophs are either phototrophs or chemotrophs. Photosynthesis is a process which utilizes carbon dioxide and water to produce sugars with the aid of sunlight. Phototrophs convert the electromagnetic energy of the sunlight into chemical energy by reducing carbon. During photosynthesis, autotrophs reduce atmospheric carbon dioxide and generate organic compounds in the form of simple sugars, storing the light energy. Photosynthesis also converts water into oxygen and releases to the atmosphere. The simple sugar glucose is polymerized to form storage sugars like starch and cellulose which are long-chain carbohydrates. Proteins and fats are produced by the polymerization of glucose as well. Examples for phototrophs include plants, algae like kelp, protists like euglena, phytoplankton and bacteria like cyanobacteria.

Figure 1: A phototrophic fern

Chemotrophs, on the contrary, use electron donors from either organic or inorganic sources as their energy source. Lithotrophs use electrons from inorganic chemical sources like hydrogen sulfide, ammonium ions, ferrous ions and elemental sulfur. Both phototrophs and lithotrophs utilize ATP generated during photosynthesis or oxidized inorganic compounds in order to produce NADPH by reducing NADP+, forming organic compounds. Most bacteria like Acidithiobacillusferrooxidans, which are an iron bacteria, Nitrosomonas, which are nitrosifying bacteria, Nitrobactor which is a nitrifying bacteria, and Algae are examples for chemolithotrophs.

Chemotrophs are mostly found on ocean floors where the sunlight is unable to reach. A black smoker, which is a hydrothermal vent found on the seabed, containing higher levels ofsulfur is a good source forsulfur bacteria.

Figure 2: A black smoker

What are Heterotrophs

Heterotrophs are organisms which are unable to fix inorganic carbon and thereby utilize organic carbon as a carbon source. Heterotrophs use organic compounds produced by autotrophs like carbohydrates, proteins and fats, for their growth. Most living organisms are heterotrophs. Examples for heterotrophs are animals, fungi, protists and some bacteria. An overview of the cycle between autotrophs and heterotrophs is shown in figure 3.

Figure 3: Cycle between autotrophs and heterotrophs

Classification of Heterotrophs

Two types of heterotrophs can be identified based on their energy source. Photoheterotrophs uses sunlight for the energy and chemoheterotrophs uses chemical energy. Photoheterotrophs, like purple non-sulfur bacteria, green non-sulfur bacteria, and Rhodospirillaceae generate ATP from sunlight in two ways: bacteriochlorophyll-based reactions and chlorophyll-based reactions. Chemoheterotrophs can be either chemolithoheterotrophs, which use inorganic carbon as the energy source, or chemoorganoheterotrophs, which use organic carbon as the energy source. Example for chemolithoheterotrophs are bacteria like Oceanithermus profundus. Examples forchemoorganoheterotrophs are eukaryotes like animals, fungi and protists. A flow chart for the determination of a species as an autotrophs or heterotrophs is shown in figure 4.

Figure 4: A flow chart discriminating autotrophs and heterotrophs

Difference Between Autotrophs and Heterotrophs

Definition

Autotrophs: Organisms that are able to form nutritional organic substances from simple inorganic substances such as carbon dioxide are referred to as autotrophs.

Heterotrophs:Organisms that are unable to produce organic compounds from inorganic sources and therefore rely on consuming other organisms in the food chain are referred to as heterotrophs.

Production of Own Food

Autotrophs: Autotrophs produce their own food.

Heterotrophs: Heterotrophs do not produce their own food.

Food Chain Level

Autotrophs: Autotrophs are at the primary level in a food chain.

Heterotrophs: Heterotrophs are at the secondary and tertiary levels in a food chain.

Manner of Eating

Autotrophs:Autotrophs produce their own food for energy.

Heterotrophs:Heterotrophs eat other organisms in order to obtain their energy.

Types

Autotrophs:Autotrophs are either photoautotrophs or chemoautotrophs/Lithoautotrophs.

Heterotrophs:Heterotrophs are either photoheterotrophs or chemoheterotrophs.

Examples

Autotrophs:Plant, algae and some bacteria are the examples.

Heterotrophs: Herbivores, omnivores, and carnivores are the examples.

Conclusion

Autotrophs and heterotrophs are two nutritional groups among organisms. The organisms which produce complex organic compounds from simple compounds in the environment are known as autotrophs. Autotrophs are the producers of the food chain. Heterotrophs are unable to fix inorganic carbons and utilize organic carbon as the carbon source. They consume other organisms as their food. The main difference between autotrophs and heterotrophs is in their carbon source.